Hi all!
First of all, thanks for the kindly reply.
I made a mistake while drawing this schematic. The schematic is updated to be more cleary.
The right value for R56 is 220 Ohms. It comes from:
The smallest amount of current to bias LT431 is 1mA and the voltage of opto LED is approximately 1V.
So, R(bias) = Vd(opto) / I(bias) = 1V / 1mA: R(bias) = 1K Ohms.
Also for R56:
Vout - Vd(led) - ( I(bias) + I(led-eol) )*R56 - V(kA-TL431) = 0V
Suposing V(ka-TL431) in the end of live equals to 3V, Vout = 12V, Vd = 1V, I(led-end of live) = 30mA and I(bias) = 1mA, we can calculate R56 as:
R56 = (Vout - V(d) - V(ka) ) / ( (Ibias) - I(led-eol) ) => ( 12V - 1V - 3V ) / ( 1mA + 30mA ) => R56 = 225 Ohms
R52 and R53 are just a voltage divider for 2.5V TL431 reference.
Have you guys already seem this approach for isolated voltage feedback using a microcontroller?
I've searched a lot about this using microcontroller but did not found anything.
Does anyone have a suggestion about this approach or another suggestion on doing this without using galvanic isolation like another transformer?
Thanks in advance!